Acquisition of information adaptable for electronic processing applications directly from printed original documents has become greatly desirable as an adjunct to electronic document production. An important reason for its desirability is the subsequent capability of manipulation of the electronically stored information for editing, compiling and using the information in forms other than that in which it was originally available. While such manipulation is, of course, available for image information produced originally and available in an electronic format, it is desirable to have a similar capability for image information not so available. Accordingly, it is desirable to have an image information input capability for such information. In addition to the production of new documents from electronically stored information, it will also be appreciated that some copying functions available in light lens-type copiers, copying images directly from original documents, may be more readily accomplished if image information is available electronically. Thus, with the capability of electronic input of information, coupled with available output devices, functions such as duplex copying, image rotation, cropping, editing, etc, are possible without the requirement of difficult mechanical manipulation of originals and copies.
A particular problem associated with electronic acquisition of image information is the speed of possible input. Heretofore, scanning arrays, i.e., linear or two dimensional arrays of semiconductor elements suitable for detection of light from an illuminated image, have been limited in size by an inability to manufacture sizable lengths thereof, thereby requiring optical magnification and focusing elements to derive an image from a document suitable for detection by the sensors of the scanning array. It has often been necessary to provide overlapping lengths of small sensors arrays to build longer lengths to accommodate document scanning. While these scanning arrays have had some success, they require extensive software manipulation to provide a correct output image, resulting in slower data or image acquisition rates. In view of the slow rate of data acquisition, relatively little work has been done on a faster document handling system for such arrangements. Recently, however, scanning arrays have become available which include a linear array of sensors extending the full width of a document. These arrays may be used to scan a document with a single pass, without magnification or optical manipulation of the image to accomodate the size to the scanning array, or software manipulation of images from overlapping arrays. These arrays are also improving in speed of image acquisition so that less time is required for each sensor to derive sufficient light information about a given image point, and transfer the information to an electronic data processor. Such arrays and their benefits over previous types of sensor arrays are described in U.S. Pat. No. 4,604,161 to Araghi, incorporated herein by reference.
In view of the above factors, it has become desirable to provide arrangements allowing faster document handling, particularly adapted to these applications of input scanners. It is desirable to provide a scanning device for scanning duplex documents, i.e., original documents having image information on both sides, for simplex documents having image information only on a single side, and for material not adaptable to be passed through sheet handling devices. In the past, this feature has been approached in input scanners in a variety of ways. As shown in U.S. Pat. No. 4,536,077 to Stoffel, an arrangement is provided with an optical system to direct light reflected from a first side of the document to a single scanning array, while the document is moving past a first position, and subsequently directing light from the second side of the document to the scanning array when it has reached a second position. The arrangement does not optimally substantially simultaneously scan the both sides of the document, requires expensive optical arrangements to transmit the image optically to the single sensor, and allows the operation of only a single sensor during a selected period of time. A disclosure entitled "Automatic Duplex Document Electronic Scanning" by Richard E. Smith, and published at Xerox Disclosure Journal, Vol. 8, No. 3, May/June, 1983 at page 263, demonstrates both side scanning of a document with two spaced apart scanning arrays arranged on opposite sides of a document path, and platen scanning by a movable carriage supporting one of the arrays. This arrangement requires multiple scanning positions and document advancement through the scanning areas at significant expense. U.S. Pat. No. 4,429,333 to Davis et al. demonstrates an arrangement which requires inversion of documents for scanning both sides thereof at a scanning position. U.S. Pat. No. 4,571,636 to Itoh demonstrates an optical arrangement for scanning both sides of a document directed along a paper path with a single scanning array, while U.S. Pat. No. 4,261,661 to Thiers shows a similar arrangement in a light lens copier. U.S. Pat. No. 4,563,706 to Nagashima and U.S. Pat. No. 4,562,485 to Maeshima demonstrate integral scanner/printer arrangements. U.S. Pat. No. 4,839,730 to Shirakoshi et al. is directed to a simplex scanning arrangement. U.S. Pat. No. 4,475,128 to Koumura shows a duplex scanning arrangement, that appears to also provide a moving scanning element. Japanese Laid Open Patent Application Nos. 62-51368, 62-51369, and 62-51370 all shows various aspects of a substantially simultaneous duplex scanning device. U.S. Pat. No. 4,743,974 to Lockwood suggests a scanner provided with a pair of scan elements arranged in opposition for substantially simultaneous duplex scanning of documents moving though a scanning station, and providing for movement of one of the scan elements for a platen scanning arrangement. All the patents and publications cited hereinabove are incorporated herein by reference.
A primary problem associated with electronic input scanners is a periodic requirement for calibration of the sensor arrangement. Because a large number of photosensitive elements make up the scanning array, uniformity of response is necessary for good imaging quality. However, varying electronic characteristics of the sensors, aging illumination sources, and varying mechanical tolerances within a scanning device all contribute to variations in the light intensity response of the sensors in the device. Frequent calibration is required against a target having a known reflectance value. U.S. Pat. No. 4,574,316 to Wilman et al. discloses a document scanner unit which rotates into at least one other scanning position to receive light reflected from a remote source. U.S. Pat. No. 4,464,681 to Jacobs et al. suggests an optical scanning system comprising a linear photodiode array which can be adjusted in position to view an optical test pattern. U.S. Pat. No. 4,605,970 to Hawkins discloses a calibration arrangement which moves an optical scanning head assembly from a reference location into a testing position to view an optical test pattern. U.S. Pat. No. 4,706,125 to Takagi discloses an image reading device comprising an integrated image reading unit and an optical sensitivity checking member which concurrently translate in unison from an inoperative position into an operative posititon during the scanning of an original. In somewhat analogous light lens copying devices, U.S. Pat. No. 4,806,977 to Mizutani et al. discloses a movable carriage housing for a scanning-type optic apparatus wherein a rack and pinion arrangement alows an upper body portion apparatus to pivto outwardly to expose a transfer station and scanning head for maintenance. U.S. Pat. No. 4,607,941 to Honda discloses an image forming apparatus containing an interchangeable process unit mounted onto a housing, which can be serviced by sliding the unit along a set of securing rails. U.S. Pat. No. 4,583,896 to Tajima et al., U.S. Pat. No. 4,500,195 to Hosono, and U.S. Pat. No. 4,588,280 to Ogawa et al. disclose electrostatic copying machines having units which rotate about a pivotal axis to expose an imaging system for maintenance and repair.
It has been found somewhat undesirable to use a calibration target on a sheet provided to the user to run through the scanning device to scan for calibration purposes. The sheets tend to degrade in image quality. Imperfect copies of the sheets may be used. The process is not automatic and thus requires operator intervention to feed the sheet. All these elements make a separate of paper an undesirable calibration target.